This invention relates to a dry analytical element for the determination of a substance existing in a liquid sample. The dry analytical element of the invention is particularly useful for the determination of an analyte contained in a biological sample in clinical assay which requires rapid and highly accurate analytical results, such as blood, cerebrospinal fluid, urine or extract of faces.
Recently, dry analytical elements composed of plural layers laminated integrally have been developed as a device for the determination of a small quantity of a liquid sample accurately, and various investigations are being done in order to improve or diversify the dry analytical elements. The dry analytical element contains all reagents for analysis, and can determine only by depositing a drop of liquid sample and measuring a color developed thereon.
Incidentally, indicator compositions used in dry analytical elements are, in general, water-insoluble. The reason is that the dye formed is resistant to diffusion because of being almost insoluble or slightly soluble to water, and as a result, accuracy is improved by the prevention of ringing (Japanese Patent KOKAI 1-320999). On the other hand, selectable reaction systems and indicator compositions for colorimetry are restricted according to the type of analyte, and sometimes, water-soluble indicator compositions must be used. In this case, a special layer for mordanting the water-soluble indicator composition is provided which increases cost and labors.